표제지
목차
국문 요약 7
영문 요약 9
제1장 서론 14
제2장 이론적 배경 17
2.1. 표면 강화 열처리 17
2.2. 질화 열처리 19
2.3. 가스 질화 21
2.4. 가스 연질화 24
2.5. 질화 및 연질화의 열역학 28
제3장 실험 방법 34
3.1. 시험편 준비 34
3.2. 가스 분위기에 따른 연질화 열처리 36
3.3. 경도 분석 38
3.3-1. 비커스 경도 38
3.4. 조직 관찰 및 분석 39
3.4-1. 광학현미경 39
3.4-2. 주사전자현미경 39
3.4-3. X-선 회절 및 전자탐침미량분석 40
제4장 결과 및 고찰 41
4.1. 열역학적 가스 분위기 41
4.2. 경도 분석 45
4.3. 조직 분석 49
4.4. 화합물층의 XRD와 상분율 55
4.5. 연질화 시 CO₂ 유량에 따른 표면의 농도 변화 60
제5장 결론 64
참고문헌 67
Table 2-1. The phase of the nitride layer formed in the gaseous nitrocarburizing 26
Table 3-1. Chemical composition (wt %) of AISI 1015 steels used in this study 35
Table 4-1. Gas flow rate and calculated data (Kn & Kc) of the gas mixture in the nitrocarburizing furnace (at 570℃) 43
Fig. 2-1. The structure of the nitride formed on the surface during gaseous nitriding 20
Fig. 2-2. A schematic diagram of the NH₃ gas decomposition reaction that occurs on the surface during gaseous nitriding 22
Fig. 2-3. Growth behavior of nitride layer formed on the surface in gaseous nitriding of iron 23
Fig. 2-4. Growth behavior of nitride layer formed in gaseous nitrocarburizing of iron 27
Fig. 2-5. Lehrer diagram in gaseous nitriding of pure iron 31
Fig. 2-6. Fe-N-C diagram at 570 ℃ 32
Fig. 2-7. Nitrogen and carbon concentrations in the ε phase as a function of nitriding potential (Kn) and carburizing potential (Kc) at 570 ℃ thermodynamically calculated by J. Kunze 33
Fig. 3-1. The schematic diagram for gaseous nitrocarburizing process 37
Fig. 4-1. Graph of thermodynamically calculated of Kn and Kc in gaseous nitrocarburizing for 5 hours at 570 ℃: (a) GN#1~#3 specimens; (b) GNC#1~#3 specimens 44
Fig. 4-2. Micro vickers hardness profile of AISI 1015 steels nitrocarburized by different gas flow: (a) GN#1~#3 specimens; (b) GNC#1~#3 specimens 47
Fig. 4-3. Microstructural evolution of nitrocarburized AISI 1015 steels by different gas flow: (a) GN#1~#3 specimens; (b) GNC#1~#3 specimens 52
Fig. 4-4. Microstructural after HCl etching of nitrided GN#1~3 specimens 53
Fig. 4-5. Microstructural after HCl etching of nitrocarburized GNC#1~3 specimens 54
Fig. 4-6. X-ray diffraction patterns for nitrocarburized specimens under different gas flow: (a) Nitriding potential (Kn); (b) CO₂ gas flow rate 58
Fig. 4-7. Phase maps analyzed by EBSD near the surface of AISI 1015 steel during nitrocarburized at 570℃ in different CO₂ gas flow rate 59
Fig. 4-8. Nitrogen and carbon contents as a function of depth below the surface determined with EPMA on the AISI 1015 steels nitrocarburized in the gas mixtures... 63